[ars]

There's a startup that did this, they posted on here about it, but I can't seem to remember how to find them.

Found this: https://news.ycombinator.com/item?id=20220288 but they don't seem to have survived.

[throwanem]

Beeminder? I've seen them mentioned here a time or two, and iirc they use a not wholly dissimilar "do the thing or lose some money" model.